1. Field of the Invention
The present invention relates to a resolver signal processing device for use in an EPS-ECU (Electronic Control Unit for Electric Power Steering) and the like.
2. Description of the Related Art
A resolver signal processing device is provided in an EPS-ECU, which is an in-vehicle electronic device, and detects a rotational angle θ of a handle shaft based on a signal from a resolver coupled to the handle shaft.
A resolver induces a phase difference specific to the resolver, between an excitation signal applied to the resolver and resolver output signals (a sine wave output signal and a cosine wave output signal), which necessitates detecting, in advance, the phase difference for detecting the rotational angle θ and canceling a value of the phase difference in detecting the rotational angle.
In initial setting at a predetermined timing such as at power-on of the resolver signal processing device and the like, the phase difference is detected. Thereafter, reference is made to the phase difference, at predetermined time intervals, to detect the rotational angle θ. In general, in order to increase accuracy in detection of the rotational angle θ, peak values of the sine wave output signal and the cosine wave output signal are detected.
In applying an excitation signal to a resolver, a conventional resolver signal processing device increments one by one a read address of a sine-wave ROM storing a sine wave for one cycle to read data which is then transmitted to the resolver (Japanese Patent Publication No. 3368837). Further, in order to compensate for the phase difference, the read starting address of the sine-wave ROM is shifted based on the phase difference.